The present invention relates to an image forming apparatus applicable to a copier, a printer and the like, and more particularly to an image forming apparatus for fine-adjusting a fixation speed of a development material in accordance with temperature control for fusing and fixing the development material.
In general, an image forming apparatus prints and records image information supplied from an image information supplying device such as a personal computer (which will be referred to as PC hereinafter) or a digital camera onto paper such as plain paper or an OHP sheet and can be applied to, for example, a color plain paper copy machine (which will be referred to as PPC hereinafter) or a printer. It is to be noted that paper may be referred to as xe2x80x9can image forming mediumxe2x80x9d in this specification according to circumstances.
The image forming apparatus for the above-described usage comprises: an image forming unit for forming an image by using a development material such as toner; a paper feeding portion for supplying paper to this image forming unit; a paper carrying portion for carrying the supplied paper; and a paper feed/paper carriage controlling portion for controlling supply/carriage of the paper to the image forming unit by the paper feeding portion and the paper carrying portion. The image forming unit includes: an image bearer for accreting the development material to be borne as an image after obtaining a latent image of an optical image formed through an optical system; a development unit for developing the latent image borne by this image bearer as an image by the development material; a transfer unit for transferring the developed image onto the paper; and a fixation unit for fixing the transferred image.
The fixation unit includes a heat roller and a press roller which sandwich the image forming medium carried by the transfer unit on the upstream side and rotate. A heat lamp for heating is provided in each of the heat roller and the press roller, and thermistors for detecting a surface temperature of each roller are provided in the vicinity of the both rollers.
The control operation for a temperature for fixing the development material in the image forming apparatus having the above-described structure will now be schematically described with reference to a flowchart of FIG. 1. In FIG. 1, the processing operation for selecting a type of the image forming medium is first carried out in accordance with a user""s choice (step ST1). In the step ST2, the type of the image forming medium is then determined, and a set temperature T is set in the fixation unit in accordance with the paper type in the step ST3. When the fixation temperature is set, a fixation temperature control sequence is started so that the temperature management is performed in accordance with a predetermined sequence in the step ST4.
In FIG. 1, as to the set temperature T, a set value is adjusted by using an adjustment sequence in the adjustment mode. The step ST10 in this adjustment sequence includes the adjustment mode step ST11 for setting the fixation temperature and the adjustment mode step ST13 for setting a fixation drive speed. When setting of the fixation temperature starts in the step ST11, the set value is stored in the step ST12 and the value is supplied as the set temperature T in the step ST3.
Upon starting control of the adjustment mode step ST13, the set value of the fixation drive speed is set in the step ST13, and the set value is stored in the step ST14. This set value is used for setting a standard speed S of the fixation drive speed in the step for setting the fixation drive speed S in the step ST15. The standard speed S of the drive speed is set separately from setting of the fixation temperature T in the step ST3. In the adjustment sequence in the step ST10, the fixation temperature T and the drive speed S are separately set without correlation, and only the set value of the fixation temperature T is taken in the control sequence. Therefore, the set value for the fixation drive speed is not used in the conventional control sequence.
Although the fixation unit fuses and fixes onto the paper the toner electrostatically absorbed on the paper, an appropriate temperature for fixation varies depending on a thickness of the paper. In case of a color image formed by using a color development material, a color having a predetermined gradation is formed by superimposing toners having different colors, e.g., yellow (Y), magenta (M), cyan (C). That is, toners having different colors are superimposed and fused to be mixed, thereby obtaining a desired color. Therefore, a temperature for fusing this color toner and a speed for fixing the toner are not separately controlled, but a technique for correlating them with each other to be fine-adjusted is demanded.
In particular, when forming an image on the surface of such as a transparent sheet used for an OHP (Over-Head Projector) and the like or forming an image on thicker paper than the plain paper, the optimum temperature management is required. Therefore, when forming an image on the image forming medium such as the thick paper or the transparent sheet, a fixation temperature optimum for the image forming medium chosen in the paper selection is fine-adjusted in advance, and an optimum temperature for each medium is set.
As a prior art relating to control over the fixation temperature and the fixation speed in such a fixation device, there are image forming apparatuses disclosed in Japanese patent application laid-open No. 138789-1994, Japanese patent application laid-open No. 219292-1995, Japanese patent application laid-open No. 220928-1996 and others. The first prior art is a technique for preventing a non-paper passing portion of the fixation roller from being unnecessarily heated; the second prior art, a technique for adjusting the fixation speed and the transfer speed in a transfer drum in accordance with each paper type; and the third prior art, a technique for preventing the fixation temperature from falling when passing the long recording paper.
In the prior art including the above-described literatures, since the heat roller and the press roller which are provided to the fixation unit thermally expand so that diameters of them increase when the fixation temperature becomes high, the speed for carrying the paper increases. When this speed exceeds the transfer speed of the transfer belt on the upstream side, the paper being carried is pulled, which generates a minute displacement at a part where transfer is carried out on the paper. Therefore, even if displacement or color shift is not generated on the part of paper where image formation was carried out earlier, displacement or color shift occurs on the part of paper where image formation was performed later, and the image formation accuracy in the entire one sheet of paper is deteriorated.
In particular, in a color image forming apparatus in which both an exposure device and a photosensitive body are united as one and multiple kinds of development materials are held in each development unit and copulatively changed over so that superimposed images are formed on the photosensitive drum, since supply positions of development materials supplied from a plurality of development units provided in accordance with respective colors are subtly displaced for example, there is a problem that displacement or color shift becomes prominent at the part of the paper where the image formation is delayed.
Further, in cases where the speed for carrying the image forming medium in the fixation unit increases even in an image forming apparatus which holds only the black development material and develops and fixes a monochrome image and there is a difference between the carriage speed and the development speed in the development unit, there occurs blur of an image or displacement of an image formation position on the part of paper where image formation is delayed, which leads to a problem such that a desired image can not be obtained.
In this manner, when a difference between the drive speed of the roller in the fixation unit and the transfer speed in the transfer unit becomes large, blur or displacement is generated on the entire sheet of paper having an imaged formed thereon.
In particular, in a color image forming apparatus in which image forming stations are arranged in parallel by a quadruple tandem mode, since a plurality of development portions supply development materials of multiple colors to the photosensitive drums for the respective colors so that images for respective colors are developed to be then transferred onto the transfer belt, displacement is prominently produced at image forming positions for respective colors to be transferred on the transfer belt when the paper carriage speed of the fixation unit increases, which results in that displacement becomes even more striking. Consequently, the color superimposition displacement becomes more prominent.
In order to solve the above-described problems, an object of the present invention is to provide an image forming apparatus capable of improving the image formation accuracy on the entire one sheet of paper by controlling a rotational velocity of a constituent element such as a heat roller or a press roller in a fixation unit whose diameter thermally expands to increase a speed for carrying an image formation medium with taking a control value based on a temperature detection value detected by the both rollers into consideration. That is, displacement or color shift is prevented at the part of paper where image formation is deteriorated in a color image forming apparatus, and color superimposition displacement is also avoided at image formation positions for respective colors to be transferred onto a transfer belt. In addition, even in case of an image forming apparatus for developing and fixing a monochrome image, blur of an image or displacement of an image forming position is prevented on the side where image formation is delayed.
To achieve this aim, an image forming apparatus according to a basic structure of the present invention is an image forming apparatus for controlling a fixation speed by fine adjustment in accordance with control of a fixation temperature, comprising: medium supplying means for supplying an image forming medium at a constant supply speed; image forming means for forming a predetermined image by using a development material based on inputted image information and holding it by an image bearer; carrying means for carrying the image forming medium supplied to the image forming means; transferring means for transferring the development material formed on the image bearer as an image by the image forming means onto the carried image forming medium; fixing means for heating the transferred development material to be fused by heating member and fixing the development material on the image forming medium; and controlling means for controlling a medium supply speed of the medium supplying means, a medium carriage speed of the carriage means, and an optimum fixation temperature of the fixing means in accordance with a type, a material and a thickness of the image forming medium, and for fine-adjusting a fixation speed of the heating member for carrying the image forming medium while following the fixation temperature whose setting varies depending on a type, a material and a thickness of the image forming medium.
In the image forming apparatus according to a first aspect of the present invention, the controlling means changes the fixation speed substantially in inverse proportion to increase of the fixation temperature so as to maintain a relative speed relationship between a transfer belt constituting the transferring means and the fixation speed of the heating means of the fixing means in the image forming apparatus according to the above-described basic structure.
In the image forming apparatus according to the first aspect, the controlling means may fine-adjust a set value for a drive speed set at the time of image formation in accordance with set values for a type, a material and a thickness of the image forming medium.
In the image forming apparatus according to the first aspect, the controlling means may fine-adjust a set value for the drive speed of the fixing means based on a measurement result measured by a temperature detection portion which is provided to the fixing means and detects a temperature of the heating member.
In the image forming apparatus according to the first aspect, the image forming means may be constituted by a plurality of image formation units provided in parallel with a transfer belt provided to the transferring means, and development materials of different colors may be filled in the respective image formation units.
In the image forming apparatus according to the first aspect, the controlling means comprises: an element for determining a type, a material and a thickness of the image forming medium; a speed set value calculation element for calculating/storing a set value for the drive speed based on a standard speed and a plurality of medium type speed correction values for setting a fixation drive speed in an adjustment mode; an element for starting the drive of a drive portion of the fixing means at the standard speed to set and change an actual drive speed of the fixing means based on a set value for a drive speed calculated by the speed set value calculation element; an element for performing fixation and heating by the heating member of the fixing means under the set actual drive speed; a temperature detection element for detecting a temperature of the heating member; a temperature set value calculation element for calculating/storing a set value for the fixation temperature based on a standard temperature and a plurality of medium type temperature correction values for setting a fixation temperature in an adjustment mode; and an element for judging whether an actual temperature of the image forming medium falls within an appropriate temperature allowable range by inputting the temperature set value calculated by the temperature set value calculation element and a temperature of the heating member detected by the temperature detection element, and for re-heating the heating member when it is out of the range, and for stopping the heating to control the fixation drive speed if it is within the range.
In the image forming apparatus according to the first aspect, detecting means for automatically detecting a type, a material and a thickness of the image forming medium is provided on the upstream side of carriage of the fixing means, and the controlling means may automatically fine-adjust the fixation speed following a change in the fixation temperature.
In the image forming apparatus according to a second aspect of the present invention, the controlling means may change the fixation speed by using a predetermined value previously set for each set value of the fixation temperature and controls to maintain the relative speed relationship between a transfer belt constituting the transferring means and the fixation speed of the heating means of the fixation means constant in the image forming apparatus according to the above-described basic structure.
In the image forming apparatus according to the second aspect, the controlling means may fine-adjust a set value for the drive speed which is set at the time of image formation in accordance with set values for a type, a material and a thickness of the image forming medium.
In the image forming apparatus according to the second aspect, the controlling means may fine-adjust a set value of the drive speed of the fixing means based on a measurement result measured by a temperature detection portion which is provided to the fixation means and detects a temperature of the heating member.
In the image forming apparatus according to the second aspect, the image forming means may be constituted by a plurality of image formation units provided in parallel with a transfer belt provided to the transferring means, and development materials of different colors may be filled in the respective image formation units.
In the image forming apparatus according to the second aspect, the controlling means may comprise: an element for determining a type, a material and a thickness of the image forming medium; a speed set value calculation element for calculating/storing a set value for the drive speed based on a standard speed and a plurality of temperature correction values gradually decreased every a fixed value for setting a fixation drive speed in an adjustment mode; an element for starting the drive of a drive portion of the fixing means at the standard speed and setting and changing an actual drive speed of the fixing means based on a set value for the drive speed which is gradually decreased every the correction value calculated by the speed set value calculation element; an element for performing fixation and heating by the heating member of the fixing means under the set actual drive speed; a temperature detection element for detecting a temperature of the heating member; a temperature set value calculation element for calculating/storing a set value for the fixation temperature based on a standard temperature and a plurality of medium type temperature correction values for setting a fixation temperature in the adjustment mode; and an element for judging whether an actual temperature of the image forming medium falls within an appropriate temperature allowable range by inputting the temperature set value calculated by the temperature set value calculation element and a temperature of the heating member detected by the temperature detection element, and for re-heating the heating member if it is out of the range, and for stopping the heating if it is within the range.
In the image forming apparatus according to the second aspect, detecting means for automatically detecting a type, a material and a thickness of the image forming medium may be provided on the upstream of carriage of the fixing means, and the controlling means may automatically fine-adjust the fixation speed following a change in the fixation temperature based on a type, a material and a thickness of the image forming medium detected by the detecting means.
In the image forming apparatus according to a third aspect of the present invention, the controlling means changes the fixation speed at a predetermined ratio in accordance with each set value of the fixation temperature and controls to constantly maintain the relative speed relationship between a transfer belt constituting the transferring means and the fixation speed of the heating means for the fixing means in the image forming apparatus according to the basic structure.
In the image forming apparatus according to the third aspect, the controlling means may fine-adjust a set value for the drive speed set at the time of image formation in accordance with set values for a type, a material and a thickness of the image forming medium.
In the image forming apparatus according to the third aspect, the controlling means may fine-adjust a set value for the drive speed of the fixing means based on a measurement result measured by a temperature detection portion which is provided to the fixing means and detects a temperature of the heating member.
In the image forming apparatus according to the third aspect, the image forming means may be constituted by a plurality of image formation units provided in parallel with a transfer belt provided to the transferring means, and development materials of different colors may be filled in the respective image formation units.
In the image forming apparatus according to the third aspect, the controlling means may comprise: an element for determining a type, a material and a thickness of the image forming medium; a speed set value calculation element for calculating/storing a set value for the drive speed based on a standard speed and a plurality of temperature correction values gradually decreased at a predetermined speed reduction ratio for setting a fixation drive speed in an adjustment mode; an element for starting the drive of a drive portion of the fixing means at the standard speed and setting and changing an actual drive speed of the fixing means based on the set value of the drive speed which is gradually decreased every the correction value calculated by the speed set value calculation element; an element for performing fixation and heating by the heating member of the fixing means under the set actual drive speed; a temperature detection element for detecting a temperature of the heating member; a temperature set value calculation element for calculating/storing a set value for the fixation temperature based on a standard temperature and a plurality of medium type temperature correction values for setting a fixation temperature in the adjustment mode; and an element for judging whether an actual temperature of the image forming medium falls within an appropriate temperature allowable range by inputting the temperature set value calculated by the temperature set value calculation element and a temperature of the heating member detected by the temperature detection element, and for re-heating he heating member if it is out of the range, and for stopping the heating if it is within the range.
In the image forming apparatus according to the third aspect, detecting means for automatically detecting a type, a material and a thickness of the image forming medium may be provided on the upstream side of carriage of the fixing means, and the control means may automatically fine-adjust the fixation speed following a change in the fixation temperature based on a type, a material and a thickness of the image forming medium detected by the detecting means.
The image forming apparatus according to a second basic structure of the present invention is an apparatus for controlling a fixation speed by fine adjustment in accordance with control of a fixation temperature, comprising: a medium supply unit for supplying an image forming medium at a constant supply speed; an image formation unit for forming a predetermined image by using a development material based on inputted image information to be held it by an image bearer; a carriage unit for carrying the image forming medium supplied to the image formation unit; a transfer unit for transferring the development material formed on the image bearer as image by the image formation unit onto the image forming medium; a fixation unit for heating the transferred development material by a heating member to be fused and fixing the development material on the image forming medium; and a control circuit for controlling a medium supply speed of the medium supply unit, a medium carriage speed of the carriage unit, and an optimum fixation temperature of the fixation unit in accordance with a type, a material and a thickness of the image forming medium, and for fine-adjusting a fixation speed of the heating member for carrying the image forming medium while following the fixation temperature whose setting varies depending on a type, a material and a thickness of the image forming medium.
With the above-described structure, according to the image forming apparatus of the present invention, when a diameter of the fixation roller may expand due to heating by the heating member of the fixation unit to increase a fixation speed, a change in speed is previously fine-adjusted in accordance with a type, a material, a thickness and others of the image forming medium, and it is hence possible to prevent pull or slack of the image forming medium caused due to increase in a temperature as well as dislocation or color shift in image formation.